Technical Library - CMC

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reducing oil consumption. Piston ring gaps should be addressed. Aim for the minimum gap on all rings, i.e. 0.014in, even if this means buying a second oversized set and filing them down. Side clearance in the ring grooves should be no more than 0.001 Sin. Excessive clearance between the skirt of the piston and the bore will also increase oil consumption. New oversize pistons are the order of the day if bore clearance is excessive. These should be supplied to the engine borer with the bare block. They can get the fit down to the manufacturer's specified clearance, having no more than 0.0005in variance in the diameter over the length of the bore.

Even before simply fitting new rings, the bores still have to be honed. This process removes the bore glaze and allows the new rings to bed in and seal. The process is carried out using special rotary stones of approximately 30 micro finishes. A good surface is essential. The bore should be left with a regular 'cross-hatching' pattern as modern practice. The surface should definitely not have a rough finish.

Valves

Valve guides are another avenue into the cylinders for oil. Excessive clearance of the valves in the guides causes oil to travel down onto the pistons or out of the exhaust

pipe. New guides and valves will be necessary to combat this. But it is also essential to fit valve stem seals. Jaguar engines were initially built without these. It is not possible to fit the correct seals to a six-cylinder engine unless we change the guides and fit the corresponding shorter valve caps. These have to be the later XJ6 type.

New inlet valve guides are supplied with a lip around the top to retain the rubber seal, but 99% of Jaguar engine builders do not fit these to the exhaust valves. The benefits of lubrication and cooling are thought to outweigh oil loss.

Burning old fossil by Andrew Turvey

Jaguar oil consumption levels are one of the more popular subjects arising in conversation with E-type owners. Jaguar engines burn oil, because oil finds its way from the sump onto the crown of the piston. Modern oil is a very determined liquid with numerous avenues open to it in a 40-year old Jaguar engine. Remember, 'modern' engine oil is cleverly designed to get into gaps only microns wide and stay there. Oil has evolved in doing this job. The latest engine oils are 50 years ahead of the engine oil control methods of the XK engine.

So, how do we prevent this tenacious liquid getting where it shouldn't? Firstly, we need to close up tolerances; in the least, a partial rebuild and new components will be the order of the day. It is not a simple case of pouring some miracle additive into the engine: consign additives to the shelf with anti-ageing creams.

Pistons

The engine has some technological catching-up to do while in pieces. The most popular avenue for oil to the piston crown is via the cylinder walls. The oil has to be present on the cylinder wall to prevent the piston skirt wearing out. However, every revolution we attempt to scrape the oil off again, at a rate of around one kilometre of oil per minute! That is a lot of oil. The piston rings are in the front line here, one set of rings in particular: the oil control rings. As fitted by Jaguar, they where very simple double-rail cast iron devices. Designers eventually realised the inadequacy of these low tension oil rings and remedied the situation by fitting a second 'oil control ring' at the base. But oil development marched on, making this modification obsolete.

piece oil control rings can take longer to bed in, unlike the original cast iron one-piece devices. So, careful running in becomes ever more critical.

The compression rings on the piston also control the oil to some extent. These could be upgraded by the use of a Dykes-type ring. L-shaped in section, they allow cylinder pressure behind them to form a better seal against the cylinder wall. From some suppliers, a separate inner expander ring is used to do a similar job

More careful checking when assembling pistons and rings pays off in

Moving forward a few more years to the bigger-bore engines, Jaguar began to fit better two-piece oil control rings. These have an expander spring behind them. Jaguar resorted to only fitting one set, as they were more successful at oil control. The same style rings are still supplied as standard with modern replacement pistons such as AE.

Better still are the more recent multi-piece devices, made up of two narrow stainless steel scrapers and a stiff expansion spring. They are usually supplied as standard with more exotic aftermarket pistons. Rings of this type are now available from a company called Deves of Hastings; these rings are a must if seeking to lower oil consumption in a 3.8 or 3.4 engine. However, power loss inevitably occurs due to the increased friction. Interestingly, Jaguar overcame the increased friction from higher tension rings by stepping up engine capacity.

A second point to note is that the better quality stainless or chrome-finished multi-

When pressing out old valve guides or fitting the new ones, we often score or broach the aluminium hole in which they sit. These minute grooves allow oil to pass down the outside of the valve guides. A drop of Loctite can be added to seal this oil path. If the existing guides are the modern type with a seal on top, you should have these 'K-lined'. This is another modern set­up that can be fitted by a firm such as VSE. A very thin bronze liner is inserted into the existing guide. It is then honed to a closer tolerance than off-the-shelf guides, again reducing oil loss.

A word of warning: if fitting high-lift cams, the underside of the valve cap can hit the top of the valve stem seal. Rob Beere has come up with another step forward: a bronze valve guide that incorporates a rubber O-ring inside the guide, giving extra clearance between the valve guide and valve cap.

Preparing to run your fresh engine

Careful preparation is required before we run a newly-ringed engine. In particular, the carburettor mixture should be weakened off as much as possible. If in any doubt, you should seriously consider having the carburettors rebuilt before fitting them on a fresh engine. It may be the case that a rich mixture caused the rings and bores to become damaged in the first place.

Running-in oil only should be used in the engine when assembling and bedding

in rings. CMC use Millers Oils' 'Pistoneeze' (Bless you!). Additives like STP are a definite NoNo: the rings may never bed in if an additive such as this is used.

When running in, the initial run should involve accelerating the car gently at low engine speeds (below 2500rpm) and shutting the throttle swiftly to draw oil up the rings, at least 10 times. Then variable driving below 3000rpm should be carried out for at least 300 miles, preferably in one session, then at no time exceed 75% of full engine speed until at least 1200 miles have been covered. Holding engines at a constant high RPM for any length of time can also prevent the rings bedding in.

The oil

Do not be in a hurry to switch from running-in oil to normal 10/40, as irreversible damage can occur such as glazing. Wait until at least 500 miles have been covered

before changing. Even 1000 miles on running-in oil is acceptable, but keep the revs down. Also, take the time to get an engine running at full temperature, even when the engine has finished running in. Thrashing a cold engine can undo all your good work instantly. You may wish to run a little cardboard in front of the radiator if the water gauge is not going above 70 degrees centigrade. The water temperature may be indicating 70 degrees but what is the oil temperature? An oil temperature gauge should always be fitted before an oil cooler is considered. Oil temperature should be around 80 degrees centigrade to get maximum oil and fuel efficiency.

As to the oil itself, I have yet to find anything better than 10W40. Semi-synthetic oil is acceptable, but definitely not fully synthetic. Oil consumption goes bananas with this oil and now you know why.

Some are using fully synthetic for racing or hard rallying, where maximum bearing protection is essential, then changing back to semi-synthetic 10W40 for road use.

For racing only I would recommend Motul 300V 15W50 fully synthetic. Race engines have modern pistons using multi-piece oil rings and stem seals on inlet and exhaust valves. In this instance we are trying to prevent oil getting into the combustion chamber because it reduces the maximum power: oil consumption is not an issue.

Issue 7

Mitchell, Peter. Restoring An E-type - Not For The Faint-Hearted Part 4

Issue 9

Mitchell, Peter. Restoring An E-type - Not for the Faint-Hearted Part 6

Issue 9

Andrew Turvey's Technical Topics

Issue 20

Griffin, Tim, CMC Column "Substructure Fabrication" (July, 2006)

Issue 24

Issue 25

CMC Colume by Andrew Turvey "The Slammer: Doors"

Issue 25

K&N E Q&A:

Issue 30

Issue 30

Issue 33

Issue 33

Issue 32

Issue 31

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Issue 36

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